Pentane
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| Names | |||
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| IUPAC name
Pentane[1]
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| Identifiers | |||
3D model (JSmol)
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| 969132 | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider | |||
| DrugBank | |||
| ECHA InfoCard | 100.003.358 | ||
| EC Number |
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| 1766 | |||
| MeSH | pentane | ||
PubChem CID
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| RTECS number |
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| UNII | |||
| UN number | 1265 | ||
CompTox Dashboard (EPA)
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| Properties | |||
| C5H12 | |||
| Molar mass | 72.151 g·mol−1 | ||
| Appearance | Colourless, transparent liquid | ||
| Odor | Odourless | ||
| Density | 626 mg mL−1 | ||
| 40 mg L−1 (at 20 °C) | |||
| log P | 3.255 | ||
| Vapor pressure | 57.90 kPa (at 20.0 °C) | ||
Henry's law
constant (kH) |
7.8 nmol Pa−1 kg−1 | ||
| Acidity (pKa) | ~45 | ||
| Basicity (pKb) | ~59 | ||
| UV-vis (λmax) | 200 nm | ||
Refractive index (nD)
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1.358 | ||
| Viscosity | 0.240 cP (at 20 °C) | ||
| Thermochemistry | |||
Heat capacity (C)
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167.19 J K−1 mol−1 | ||
Std molar
entropy (S⦵298) |
263.47 J K−1 mol−1 | ||
Std enthalpy of
formation (ΔfH⦵298) |
−174.1–−172.9 kJ mol−1 | ||
Std enthalpy of
combustion (ΔcH⦵298) |
−3.5095–−3.5085 MJ mol−1 | ||
| Hazards | |||
| GHS labelling: | |||
   
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| Danger | |||
| H225, H304, H336, H411 | |||
| P210, P261, P273, P301+P310, P331 | |||
| NFPA 704 (fire diamond) | |||
| Flash point | −49.0 °C | ||
| Explosive limits | 1.4–8.3% | ||
| Lethal dose or concentration (LD, LC): | |||
LD50 (median dose)
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| Related compounds | |||
| Supplementary data page | |||
| Pentane (data page) | |||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Pentane is an organic compound with the formula C5H12 — that is, an alkane with five carbon atoms. The term may refer to any of three structural isomers, or to a mixture of them: in the IUPAC nomenclature, however, pentane means exclusively the n-pentane isomer; the other two being called "methylbutane" and "dimethylpropane". Cyclopentane is not an isomer of pentane.
Pentanes are components of some fuels and are employed as specialty solvents in the laboratory. Their properties are very similar to those of butanes and hexanes.
Isomers
| Common name | normal pentane unbranched pentane n-pentane |
isopentane | neopentane |
| IUPAC name | pentane | 2-methylbutane | 2,2-dimethylpropane |
| Molecular diagram |
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| Skeletal diagram |
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Industrial uses
Pentane is one of the primary blowing agents used in the production of polystyrene foam.
Because of its low boiling point, low cost, and relative safety, pentane is used as a working medium in geothermal power stations. It is added into some refrigerant blends as well.
Laboratory use
Pentanes are relatively inexpensive and are the most volatile alkanes that are liquid at room temperature, so they are often used in the laboratory as solvents that can be conveniently evaporated. However, because of their nonpolarity and lack of functionality, they can only dissolve non-polar and alkyl-rich compounds. Pentanes are miscible with most common nonpolar solvents such as chlorocarbons, aromatics, and ethers. They are also often used in liquid chromatography.
Physical properties
| Isomer | MP (°C) | BP (°C) | Density (g/L) |
|---|---|---|---|
| n-pentane | −129.8 | 36.0 | 621 |
| isopentane | −159.9 | 27.7 | 616 |
| neopentane | −16.6 | 9.5 | 586 |
The boiling points of the pentane isomers range from about 9 to 36 °C. As is the case for other alkanes, the more branched isomers tend to have lower boiling points.
The same trend normally holds for the melting points of alkane isomers, and indeed that of isopentane is 30 °C lower than that of n-pentane. However, the melting point of neopentane, the most heavily branched of the three, is 100 °C higher that of isopentane. The anomalously high melting point of neopentane has been attributed to the better solid-state packing assumed to be possible with its tetrahedral molecule; but this explanation has been challenged on account of it having a lower density than the other two isomers.[3]
The branched isomers are more stable (have lower heat of formation and heat of combustion) than normal pentane. The difference is 1.8 kcal/mol for isopentane, and 5 kcal/mol for neopentane.[4]
Rotation about two central single C-C bonds of n-pentane produces four different conformations.[5]
Reactions
All pentane isomers burn with oxygen to form carbon dioxide and water:
- C5H12 + 8 O2 → 5 CO2 + 6 H2O
As with other hydrocarbons, pentanes undergo free radical chlorination:
- C5H12 + Cl2 → C5H11Cl + HCl
Such reactions are unselective; with n-pentane, the result is a mixture of the 1-, 2-, and 3-chloropentanes, as well as more highly chlorinated derivatives. Other radical halogenations can also occur.
While n-butane is the conventional feedstock in the production of maleic anhydride, n-pentane is also a substrate:
- CH3CH2CH2CH2CH3 + 5 O2 → C2H2(CO)2O + 5 H2O + CO2
References
- ^ "pentane - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification and Related Records. Retrieved 18 December 2011.
- ^ Record of n-Pentane in the GESTIS Substance Database of the Institute for Occupational Safety and Health, accessed on 19 April 2011.
- ^ a b James Wei (1999), Molecular Symmetry, Rotational Entropy, and Elevated Melting Points. Ind. Eng. Chem. Res., volume 38 issue 12, pp. 5019–5027 doi:10.1021/ie990588m
- ^ From the values listed at Standard enthalpy change of formation (data table).
- ^ Roman M. Balabin (2009). "Enthalpy Difference between Conformations of Normal Alkanes: Raman Spectroscopy Study of n-Pentane and n-Butane". J. Phys. Chem. A. 113 (6): 1012. doi:10.1021/jp809639s. PMID 19152252.
External links
- International Chemical Safety Card 0534 at ILO.org
- NIOSH Pocket Guide to Chemical Hazards at CDC.gov
- Material safety data sheet for Pentane at Ox.ac.uk
- Phytochemical data for pentane at Ars-grin.gov